During the summer you can prolong a plant's flowering time by regular dead heading. But also by pruning and cutting back, you can also get a second flush of flowers. 

Wisteria needs to be pruned twice a year without fail essentially to make it flower, and it will often produce a second flush around July. The image on the right shows the Wisteria just starting to produce a second, lighter and much less prolific flush of flowers but nice to see and enjoy. This second flush has been created by pruning and good weather conditions: tips and advise on growing Wisteria and how to make it flower.

Also in the image right is a second flush of Delphinium, again much smaller and less blooms, but still flowering in late July. To do this you need to cut off the main spent flowering shoot and leave the side shoots to develop more flowers. Removing the spent flower head to a lateral leaf or bud will also work for Achillea, Lupins and Digitalis the foxglove.

Some plants can look very messy after flowering such as  Geranium ibericum and Alchemilla mollis which are unlikely to flower again the foliage can look very tatty. With these I cut them down almost to the base, but check carefully as there will be young foliage coming through and within 10-14 days the plant will have produced some smart looking new green foilage which looks much better as in the image below. Just a couple of weeks ago this was almost bare earth.

There are of course plants which only flower once Agapanthus,  Iris, Peony but most plants will benefit from either dead heading, removal of the spent flower spikes, or cutting back tired looking foliage.

This can also work in the veg plot with a good summer. It is perfectly possible to get a second crop of broad beans, When the plant has produced all its pods cut it down close to the ground but not level, look at the plant for signs of lateral growth and cut above it. Over a few weeks the broad bean will re grow, flower and with luck produce a second light crop but perfectly edible. More about how to get a second crop of broad beans